This invention relates to an improved method for eliminating radioactive and stable isotopes, and other deleterious materials including certain organic materials, from radioactive waste liquids and other liquids containing them. More particularly, this invention relates to the elimination of such deleterious materials from liquids by a novel filtration method utilizing novel filter/demineralizer pre-coating compositions.
The handling and disposal of radioactive waste materials is a continuing and growing problem in nuclear energy installations and operations. As nuclear energy use increases, the need for more efficient waste handling techniques is being raised to a higher priority.
Most radioactive waste exists in liquid form, obtained, for example, during the normal operation of nucelar reactors, and in the manipulation and handling of radioisotopes. Many of the activation fission and corrosion products present in radioactive waste liquids have relatively short half-lives and present no problems with regard to safe disposal. However, disposal problems are quite in evidence when the waste liquids contain such radioisotopes as radiocesium and radiocobalt, which have substantially longer half-lives and occur in higher concentrations in nuclear facilities.
Ultimate disposition of radioisotope elements in radioactive wastes is customarily effected by burial in the ground. For ground burial, the waste must be a solid or, in the case of a liquid, be solidified.
Various methods have been suggested in the past for effecting concentration of radioactive liquid waste, examples of which are simple evaporation of the liquid components, precipitation of the radioactive elements, and fixation of the radioactive elements on solids. However, utilization of prior art techniques have not proven entirely satisfactory in large scale operations. For example, the concentration of radioactive liquid wastes, particularly low-level wastes, by evaporation is economically disadvantageous when large volumes of liquid waste are processed. Problems also are experienced with foaming, carryover of volatile fractions, and the corrosive and scaling nature of the waste on evaporator components.
One of the most practical prior art methods used to treat liquid radioactive wastes prior to disposal has been the fixation of the radioactive elements in the liquid waste on a solid, as by adsorption or ion-exchange, permitting the liquid to be safely released to normal environmental liquid waste disposal sites or returned to the primary plant system as make-up water.
In accomplishing the separation of radioactive elements by such methods, the contact of the liquid waste with certain naturally-occurring materials, such as inorganic zeolites, which exhibit capability in the selective adsorption of radioactive elements, has been utilized. Recommended for the fixation of radiocesium in the past have been such materials as montmorillonite, erionite and the like. Naturally-occurring materials, such as these, generally exhibit limitations as adsorbent materials due to such factors as impurities and composition inconsistencies. These properties tend to result in less than desirable economic advantages when purification is attempted and, in some instances, loss of stability under processing conditions. A problem that has existed in the use of inorganic zeolites is that the solubility of these materials is such that undesirable contaminants were introduced when treating high purity streams. As a result it was necessary for a separate ion exchange resin unit to be used downstream for the removal of these contaminants, increasing the cost of treatment considerably.
In view of the foregoing, it is an object of this invention to provide an improved method for the removal of radioisotopes and stable isotopes from radioactive waste liquids.
Another object of this invention is to provide an improved method which is particularly effective in the removal of radioisotopes such as cesium, cobalt and other ionic constituents and organic molecules from radioactive waste liquids containing the same.
Still another object of the invention is to provide a method for the removal of radioisotopes and stable isotopes from radioactive waste liquids through the use of a single processing step.
Still another object of this invention is to provide a method by which organic molecules in solution can be removed in a pre-coated filter-demineralizer through the use of zeolitic and ion exchange resin materials.
It is a further object of this invention to provide an improved method for the removal of radioisotopes and stable isotopes from radioactive waste liquids wherein separation is effected both more efficiently and more economically than is attainable with prior art methods.
Further objects and advantages of the invention will become apparent from the description which follows.